Currently, there is a strong interest in the packaging industry in biaxially oriented containers made from poly(ethylene terephthalate) (PET). Containers constructed of PET have recently found wide acceptance in the packaging of food stuffs, medicines, and consumer products.
Despite the popularity of PET in container manufacture, there are several drawbacks to the use of PET. Although PET is usually considered a high barrier polymer, the use of PET containers for beer has heretofore been avoided due to the rapidity with which beer loses its flavor, due largely to oxygen migration into the bottle.
U.S. Pat. Nos. 4,049,361; 4,098,769; and 4,110,315 all to Santos Go, relate to copolyesters containing sulfone units therein and having a glass transition temperature of 75.degree. C. or higher. Unoriented poly(ethylene terephthalate) generally has a glass transition temperature of about 72.degree. C. Although the copolyesters of Go tend to have lower oxygen and carbon dioxide permeabilities than pure PET, they also have higher glass transition temperatures. Moreover, they do not relate to any multi-layer articles or to poly(ethylene isophthalate) layers therein having glass transition temperatures of less than 70.degree. C.
U.S. Pat. No. 4,145,517 also to Santos Go relates to copolymers of polyesters also containing sulfone units therein. The glass transition temperature of the copolymers is at least 120.degree. C. This patent also does not relate to multi-layer polyester articles or to layers therein having low glass transition temperatures.
The Kirk-Othmer Encyclopedia of Chemical Technology, Third Edition, 1978, Volume 3, at page 480, states that with regard to factors affecting barrier properties, a truly good barrier polymer must have some degree of polarity such as contributed by nitrile, etc., groups, high chain stiffness, inertness, close chain-to-chain packing, order, crystallinity, or orientation, some bonding or attraction between the chains, and a high glass transition temperature. Furthermore, at page 487, it is stated that permeation of carbon dioxide is an important factor in determining a high barrier polymer, especially for the use of highly carbonated beverages since carbon dioxide permeability rates are three to four times that of oxygen in almost all polymers. At page 490, it is stated that many foods are very sensitive to oxidation which causes flavor changes or discoloration. Moreover, it is noted that loss of 10 percent or more of carbonation can easily be detected by taste and that beer flavor is affected by oxygen levels of less than 2 parts per million.
U.S. Pat. No. 2,965,613 to Milone relates to copolymers of ethylene terephthalate and ethylene isophthalate. This patent is not pertinent in that it does not relate to multi-layer articles having good barrier resistance to oxygen or carbon dioxide.
U.S. Pat. No. 3,733,309 relates to biaxially molded poly(ethylene terephthalate) with regard to making containers.
U.S. Pat. No. 3,955,697 relates to a multi-layer, hollow plastic container having an inside and outside layer of heat-resistant plastic and an intermediate barrier layer of a thermoplastic material so that the barrier layer progressively softens, or perhaps melts, and reforms in place upon exposure to elevated temperatures and subsequent cooling to ambient temperatures. This patent does not relate to any polyester layer whatsoever and hence is not pertinent.
U.S. Pat. No. 4,234,708 relates to the use of chain branching agents to produce polyethylene iso/terephthalate having at least 85 percent by weight of terephthalate therein. Thus, this patent is not pertinent since it utilizes very small amounts of isophthalic acid.
Although numerous multi-component or layered plastic articles have been made, none of them relate to solely a polyester multi-component article having very high barrier properties. For example, the following Chem Abstract numbers relate to multi-layer articles made from plastics other than polyesters: 84:32117u; 88:171414j; 141292b; 84:32124u; and 86:141006u. Various other Chem Abstract articles incorporate a layer or a portion of a layer in a multi-component article of polyester, as for example 85:144321h; 141229m; 91:75463r; 86:141090s; 84:31960b; 92:112365d; 92:149089f; 91:194287w; 92:23805e; and 87:7135c. However, none of these articles relate to multi-layer polyester articles. It is further noted that generally most high barrier plastics have very high melt viscosities, making it very difficult to form them into a thin layer as required for multi-layer article production. Other plastics decompose when heated to a temperature such that they are extrudable. Still, other plastics have very poor hot melt processabilities, or have high relt temperatures which induce crystallizability of PET when injection coated over a PET preform.
An article entitled "Gas Barrier Property and Multilayer Blown Bottle" by Akira Kishimoto, Japan Plastics Age, November-December, 1976, pages 21-25, relates to a discussion of multi-layer blown bottles made by the coextrusion technique. An article entitled "Current Situations and Future Prospects of Plastic Bottles," also by Akira Kishimoto, November-December, 1976, Japan Plastic Age, relates to various types of plastics which have been utilized in making containers such as bottles. However, neither of these articles relates to multi-layer bottles utilizing solely polyester and in fact states on page 20, of the second article, that all of the multi-layer bottles lack clarity and appearance as compared with those of stretched PET and PVC.